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Biomedical subjects

S Kochhar

Publications and source records attributed to S Kochhar.

At least 55 records · Page 3Linked to original sources
PubMed1989

Assay for aliphatic amino acid decarboxylases by high-performance liquid chromatography.

A sensitive and rapid assay for aliphatic amino acid decarboxylases based on separation of the product from the substrate by ion-pairing reversed-phase high-performance liquid chromatography and subsequent fluorometric detection has been developed. The resolution of substrates and products of seven amino acid decarboxylases, namely, arginine, aspartate, 2,6-diaminopimelate, histidine, glutamate, lysine, and ornithine decarboxylase, is complete within 15 to 35 min of isocratic elution. The limit of detection for the product is 40 pmol. The applicability of the procedure was assessed with glutamate decarboxylase. The formation of the product 4-aminobutyrate proved to be linear with time and protein concentration. The method allows the time course of the reaction to be followed in a single assay and works well with crude extracts of bacteria or tissues.

Carboxy-Lyases↗
PubMed1989

Amino acid analysis by high-performance liquid chromatography after derivatization with 1-fluoro-2,4-dinitrophenyl-5-L-alanine amide.

Amino acids are quantitatively determined by precolumn derivatization with 1-fluoro-2,4-dinitrophenyl-5-L-alanine amide and reversed-phase high-performance liquid chromatography with photometric detection at 340 nm. Excellent chromatographic resolution of a mixture of the derivatives of 20 amino acids including proline and cystine is achieved within 110 min by linear gradient elution with acetonitrile in 13 mM trifluoroacetate plus 4% (by vol) tetrahydrofuran. The limit of detection is 50 pmol. Amino acid analyses of acid hydrolysates of the several proteins gave results equivalent to those obtained by conventional ion-exchange-based amino acid analysis. The simplicity of the procedure allows its use on any multipurpose high-performance liquid chromatographic system.

Alanine↗
PubMed1988

The enantiomeric error frequency of aspartate aminotransferase.

The enantiomeric error frequency of aspartate aminotransferase (mitochondrial isoenzyme from chicken) was assessed by adding the enzyme in high concentration (0.89 mM) to a mixture of L-glutamate and 2-oxoglutarate (12 and 1.2 mM, respectively, at pH 7.5 and 25 degrees C). The substrates continuously undergo the transamination cycle under these conditions. Thereby, L-glutamate is progressively racemized, a 1:1 ratio of two enantiomers being reached within 240 h. The enantiomeric error frequency, i.e. the ratio of the rate of D-glutamate production and the rate of the transamination reaction with glutamate and 2-oxoglutarate as substrates, is 1.5 x 10(-7). D-Glutamate is also converted to a 1:1 racemic mixture. The racemizing activity of a mixture of free pyridoxal 5'-phosphate and pyridoxamine 5'-phosphate is about two orders of magnitude lower than that of aspartate aminotransferase. The error frequency of the enzyme in the case of the C4 substrate pair aspartate and oxalacetate is 3.4 x 10(-8), i.e. 4 times lower than that with the C5 substrate pair.

Animals↗
PubMed1987

The stereospecific labilization of the C-4' pro-S hydrogen of pyridoxamine 5'-phosphate is abolished in (Lys258----Ala) aspartate aminotransferase.

Reconstitution of wild-type apoaspartate aminotransferase from Escherichia coli with [4'-3H]pyridoxamine 5'-phosphate results in stereospecific release of the pro-S C-4' 3H to the solvent. The reaction follows first-order kinetics (t1/2 = 15 min at pH 7.5 and 25 degrees C), its rate constant being similar to that found previously with mitochondrial aspartate aminotransferase from chicken (Tobler, H.P., Christen, P., and Gehring, H. (1986) J. Biol. Chem. 261, 7105-7108). Substituting the active site residue Lys258 by alanine via site-directed mutagenesis yields a catalytically inactive enzyme (Malcolm, B. A., and Kirsch, J. F. (1985) Biochem. Biophys. Res. Commun. 132, 915-921). This mutant enzyme fails to release any measurable 3H from bound [4'-3H]pyridoxamine 5'-phosphate. The data are consistent with earlier proposals that Lys258 is indispensable for the ketimine/aldimine tautomerization, and corroborate the previous conclusion that 3H exchange from enzyme-bound pyridoxamine 5'-phosphate mechanistically corresponds to the deprotonation at C-4' of the ketimine intermediate during the transamination reaction.

Alanine↗
PubMed1987

Detection of aspartate kinase in rat liver and its activation by Ca++ and calmodulin.

The enzyme aspartate kinase (EC 2.7.2.4) has been detected in rat liver (animal tissue) for the first time. This enzyme, like the aspartate kinase from bacteria and plants is inhibited by lysine and threonine. Further, the activity of the enzyme is stimulated over two fold by Ca++ and calmodulin and inhibited by EGTA, a Ca++ chelator and trifluoperazine, an anti-calmodulin compound.

Animals↗
PubMed1985

Chemical modification of liquefying alpha-amylase: role of tyrosine residues at its active center.

Liquefying alpha-amylase from Bacillus amyloliquefaciens was inactivated by treatment with tetranitromethane and N-acetylimidazole. The loss of activity occurred with modification of five tyrosine residues. Preincubation of the enzyme with either the substrate or the competitive inhibitor at saturating levels provided complete protection against inactivation. However, the presence of substrate/inhibitor in the reaction mixture protected only two of the five modifiable tyrosine residues, suggesting the involvement of only two tyrosine residues at the active center. This was confirmed when hydroxylamine treatment of the acetylated enzyme fully restored the enzymatic activity. Both nitration and acetylation increased the apparent Km of the enzyme for soluble starch, which indicated that the tyrosine residues are involved in substrate binding. Reduction of nitrotyrosine residues to aminotyrosine residues failed to restore the enzymatic activity. So, the loss of activity on modification of tyrosine residues was ascribed to conformational perturbances and not simply to the changes in the ionic character of tyrosine residues.

Acetylation↗
PubMed1985

An active center tryptophan residue in liquefying alpha-amylase from Bacillus amyloliquefaciens.

Liquefying alpha-amylase from Bacillus amyloliquefaciens was inactivated on treatment with N-bromosuccinamide. Preincubation of the enzyme with either of the substrate, or competitive inhibitor provided significant protection against inactivation. The relationship between activity loss and the number of tryptophan residues modified, as well as presence of substrate/inhibitor in the reaction mixture, demonstrated that only one of three modifiable tryptophan residues is at or near the active center. The apparent Km of the modified enzyme for soluble starch increased manifold, thus implicating the sensitive tryptophan residue in the substrate binding region of the enzyme.

Bacillus↗
PubMed1985

Active site studies on Bacillus amyloliquefaciens alpha-amylase (I).

Modification of liquefying alpha-amylase by diethylpyrocarbonate or its photo-oxidation in the presence of rose bengal caused rapid loss of enzyme activity. The photo-oxidation followed pseudo-first-order kinetics giving maximal value at pH 8.0. The photo-oxidized enzyme showed a characteristic increase in absorbance at 250 nm which was directly proportional to the extent of inactivation. Diethylpyrocarbonate at low concentration at pH 6.0 and 30 degrees C completely inactivated alpha-amylase. Inactivation followed pseudo-first-order kinetics. The reaction order with respect to inactivation by diethylpyrocarbonate-modified enzyme showed increased absorbance at 240 nm which was reversed completely upon treatment with NH2OH at 30 degrees C for 16 hr. Calculating the histidine residues being modified from the increase in absorbance at 240 nm showed that three residues were ethoxyformylated on treatment with diethylpyrocarbonate, of which only one was found at the active site. Substrate and competitive inhibitor protects the enzyme against both, photo-oxidation, and modification by diethylpyrocarbonate, confirming that histidine plays an essential role at the alpha-amylase active site.

Bacillus↗
PubMed1984

An active-site carboxyl group in liquefying alpha-amylase: specific chemical modification.

Bacillus amyloliquefaciens alpha-amylase activity is pH-dependent and the plot log (Vmax/Km) versus pH implicated a carboxyl group of aspartic acid/glutamic acid at the active site. Chemical modification of alpha-amylase with EDC confirmed this view. Further, analysis of inactivation kinetics showed that modification of a single carboxyl group led to complete loss of the enzymic activity.

Bacillus↗
PubMed1979

Blind and disabled persons awarded federally administered SSI payments, 1975.

State agencies made medical determinations on 975,000 applications filed by the blind and disabled in 1975. Forty percent were found eligible for federally administered payments, and 60 percent were found ineligible. Nine out of 10 of the awardees were adults. Forty percent of these adults either had no occupation or no occupation was reported. Among both adults and children, the leading cause of disability was mental illness. Nearly 1 out of 3 adults was awarded benefits on the basis of mental disorders. The proportion of children determined disabled by mental illness was about twice that of adults. More than one-half of all children awarded benefits were mentally retarded. Among adults, the second most frequent disabling impairment was cardio-vascular disease; among children, it was diseases of the nervous system and sense organs.

Adult↗
PubMed1979

Appeals under the SSI Program: January 1974-August 1976.

This study of appeals under the supplemental security income (SSI) program has several purposes: (1) To describe the appellate process and provide information on those requesting appeals (including reason for eligibility, program status, and age) and (2) to determine the relationship between these characteristics and the decisions at the three stages of the appellate process. About 312,000 reconsideration requests were processed from January 1974 to August 1976. These requests had been filed by adult and child SSI applicants who disagreed with the initial determinations of the Social Security Administration. Disabled persons requested nearly 95 percent of these reconsiderations. Approximately one-third of the applicants whose initial determination was reaffirmed after reconsideration then requested a hearing. Ninety-seven percent of these requests were filed by disabled persons. For those cases in which the earlier decisions were reaffirmed after hearings, 9,300 applicants requested a review by the Appeals Council. Eighty-two percent of these requests were denied.

Adolescent↗
PubMed1977

SSI recipients in domiciliary care facilities: federally administered optional supplementation, March 1976.

Under the supplemental security income program, federally administered payments amounting to $24.7 million were made in March 1976 to 107,000 persons who were residing in domiciliary care facilities and under other supervised living arrangements. These persons were unable to function under totally independent living arrangements but did not require medical or nursing care on a regular basis. Of the total, $9.5 million was represented in Federal SSI payments and $15.2 million came from optional State supplements--with California paying $6.2 million and New York $4.6 million. The average payment to the residents of these facilities was $232 a month. Comparable data for four States show greater caseload growth for persons in domiciliary care facilities and under other supervised living arrangements than for the total SSI population. Nearly two-thirds of the States are adding funds to Federal SSI payments for persons under such care. Data are available, however, only from Social Security Administration program records for those States that have elected Federal administration of their optional programs.

Adolescent↗
PubMedDate not supplied

Cyclodialysis cleft diagnosed by conventional ultrasonography.

This case report describes the diagnosis and management of a traumatic cyclodialysis cleft, in the absence of newer investigating modalities like ultrasonic biomicroscopy (UBM). This entity is frequently difficult to recognize clinically owing to the extreme hypotony and media haze that these patients usually present with, which makes gonioscopy particularly taxing. Adding to the diagnostic dilemma is the difficulty in delineating the lesion ultrasonically due to the extreme anterior location of the cleft. In these situations, high frequency ultrasound has been found to be extremely helpful, but the availability of such sophistication is difficult. Presented here is demonstration of the cleft with a microconvex ultrasound probe of 9 MHz frequency. The patient was successfully managed conservatively. This modality could prove to be a valuable adjunct to the diagnosis of such cases even in the situations of nonavailability of high frequency ultrasonography.

Adult↗
PubMedDate not supplied

Tuberculosis of the parotid gland.

Tuberculosis of the parotid gland is a rare entity. Only about a hundred cases have been reported till date, mostly from parotidectomy specimens. The present case was diagnosed by fine needle aspiration and treated successfully by short-course antitubercular chemotherapy. An early diagnosis can avoid parotidectomy, which can be a hazardous procedure in a medically treatable condition.

Female↗